This disclosure pertains to video content control detection systems, and in particular, to Macrovision Corp. compliant “color stripe” signal detectors of the type often embedded in commercially available integrated chip sets used in video recorders or other Macrovision Corp. compliant video devices. It is known that such a color stripe detector is able to read or detect properly the Macrovision Corp. color stripe copy protection signals when an entire video color burst is phase modified or when a majority of the color burst is so phase modified.
However, such a color stripe signal, well known from Ryan U.S. Pat. No. 4,577,216 incorporated by reference in its entirety, is primarily a copy protection video signal, which is generally playable on a TV (television) set, but which causes an analog video cassette recorder (VCR) to play back a recorded signal with color errors. In the PAL TV standard, synthesizing a playable color stripe signal with negligible display artifacts while providing an effective copy protection signal on a VCR or other video tape recorder is a challenge. For example, the more effective the color stripe signal is on a particular video tape recorder in preventing copying, the more likely that playability artifacts (on a TV display) are noticeable. Some PAL color stripe processes are not commercially viable because of such display artifacts, and thus not implemented.
In recent years with the decline in VCR sales or usage, newer video recorders such as digital personal video recorders have replaced the VHS (analog) video tape recorders. These newer digital video recorders use a different type of recording system, which includes a detection system as explained above for reading or detecting the incoming color stripe signal. Once a color stripe copy protection signal is detected in a video signal, a content control command is generated, such as “Prohibit Recording/Viewing”. A compliant device can then accept the content control command to stop recording or to replace/mute the program video signal with another signal such as a blue screen. Brill et al., U.S. Pat. No. 6,600,873 incorporated by reference in its entirety, discloses how a device such as a video recorder includes special detection circuitry to detect the color stripe process and producing in response a control signal which disables the recorder, to prevent further recording. The same concept is embodied in commercially available integrated circuit video decoders which detect the color stripe process and in response issue commands to control operation (such as no recording) of a device such as a video set top box, personal video recorder or other in which the video decoder is installed. Such video decoders are generally referred to as “Macrovision compliant”. Examples are the Texas Instruments TVP5146 video decoder and the Micronas AVF4910B video pixel decoder. See also Macrovision Corp. patent publication WO 2005/039176A1 disclosing use of analog copy protection to encode permitted use information.